Joining dissimilar materials, such as metallic and non-metallic materials, often presents a variety of technical challenges. Not only are dissimilar materials resistant to many types of conventional joining methods, even joints that are formed may not be able to withstand substantial stress or harsh environmental conditions. These challenges are particularly true for electrical equipment that is placed outdoors, however, harsh environmental factors such as high temperatures can also be present in indoor environments. For example, in the case of capacitor tanks, there is a need to join non-metallic capacitor bushings to metallic terminal caps and metallic tank covers. Capacitor bushings serve several functions. The primary function of the bushing is to isolate electrical leads, which may be at thousands of volts of electric potential, from the metal body of the capacitor tank and from each other. The capacitor bushing is also used to isolate the contents on the inside of the capacitor from the outside environment. It is necessary to protect the internal capacitor components from contact with the exterior environment since contamination by moisture or dust may degrade the dielectric capacitor fluid and lead to capacitor failure. Also, the capacitor bushing seals the dielectric fluid inside the capacitor and prevents it from escaping to the environment.
Currently, there are several different approaches that can be used to join these metallic and non-metallic surfaces. One example is soldering. Soldering the capacitor bushings typically involves a complicated procedure wherein two coats of a thick silver-based painted film are applied to the capacitor bushing in a carefully controlled process. The coats of paint are dried and then the capacitor bushing is fired at high temperatures under carefully controlled conditions. After the firing process, the capacitor bushing can be soldered to metallic components. The soldering process can be complex, labor-intensive and expensive.
An alternative approach to joining metallic and non-metallic surfaces is to use mechanical components and fasteners. However, mechanical fastening requires additional components which add expense and complexity to the capacitor tank and mechanical fasteners may provide insufficient joint strength for some applications and may lose sealing integrity under mechanical stress over the life of the capacitor as it is exposed to harsh environmental conditions.
Accordingly, there is a need for an improved method for joining dissimilar materials such as the metallic and non-metallic components used to manufacture capacitor tanks. Specifically, there is a need for an improved technique for joining metallic and non-metallic components that is a less expensive and simpler process and that produces a stronger joint with more reliable sealing properties during the life of the capacitor.